1. Technical Field
This disclosure relates to an extrusion molding method of an extrusion press that exhausts air inside a container after a billet is loaded into the container when aluminum alloy or the like is extrusion molded by an extrusion press. More particularly, the disclosure relates to an extrusion molding method of an extrusion press that continuously extrudes a billet in succession to a preceding step. Furthermore, the disclosure relates to an improved extrusion molding apparatus for effectively and efficiently extruding a billet without entrapping air by the steps of closing the press by exhaust means detachable from the extrusion stem during extrusion molding of aluminum alloy, etc, by the extrusion press, simultaneously pushing a seal member disposed on the container side of the exhaust means to the container by a push device and exhausting air between the container and the billet before the billet is extruded.
2. Description of the Related Art
When aluminum alloy or the like is extrusion molded by an extrusion press, for example, a billet having a diameter smaller than an inner diameter of a container is first loaded into the container and is pushed into a die by an extrusion stem disposed at the back of the billet inside the container, or in other words, is subjected to so-called “upset”. In this instance, the billet is crushed and air in the gap between the container and the billet is compressed. When exhaust of this compressed air outside the container is insufficient before extrusion of the billet, blisters occur in the resulting molding.
To overcome this problem, Japanese Unexamined Patent Publication (Kokai) No. 10-128432 describes a method for sucking and exhausting air by closing and sealing the gap between the container and the extrusion stem by split sealing means, advancing the extrusion stem to push the billet and sucking and exhausting air in the gap between the container and the billet before extrusion until upset is completed.
Extrusion molding of the prior art is carried out by the following method. To begin with, a billet cast and cut into a predetermined length is heated to a predetermined temperature by heating means such as a billet heater, and is loaded into a container in a state in which the billet is heated and its temperature is maintained. After air inside the container is exhausted, the billet is pressure fed forward by the extrusion stem. However, oxides and segregates of the outer peripheral portion of the billet and air are entrapped in the center portion of the billet on the contact surface of the billet with the extrusion stem when the billet is upset.
Therefore, to prevent the outflow of the oxides and the segregates to the extrusion molding, the extrusion molding operation is conducted in such a manner as to leave a predetermined length of unmolded portion and a discard and after the discard is discharged from the container and is cut, the next billet is loaded into the container and extrusion molding is continued.
Consequently, a non-extrusion time such as during an opening operation of the container till extrusion of a next billet, separation and cutting of the discard, etc, is extended and the efficiency of extrusion molding deteriorates.
Also, the container must be moved to remove the discard and it is difficult to maintain the positional accuracy of the container.
When a billet having a diameter a little smaller than an inner diameter of a container is loaded into the container and is pushed into a die by an extrusion stem disposed at the back of the billet inside the container, or in other words, when the billet is subjected to so-called “upset”, the billet is crushed and air between the container and the billet is compressed. To vent the compressed air to the outside of the container from the side of a fix dummy block of the extrusion stem, a known exhaust apparatus has the following construction. Namely, a side end surface of a ring-like seal portion and an outer peripheral surface of the extrusion stem are allowed to simultaneously come into close contact with each other through the ring-like seal portion disposed on an end face of the container, into which a billet is loaded, on its extrusion stem side, a two-split seal block disposed in the direction crossing an axial direction of the extrusion stem, a seal member bonded to the contact surface of the seal block when the seal block is closed and a seal member disposed on the end face of the seal block on the extrusion stem side, and push means for pushing the seal member disposed on the end face of the seal block on the container side to the ring-like seal portion is disposed in such a manner as to be capable of moving in the axial direction of the extrusion stem. In the case of this construction, the above-mentioned patent document Japanese Unexamined Patent Publication No. 10-128432 describes a method of sucking exhaust air from a gap between the outer peripheral surface of the fix dummy block and the inner peripheral surface of the container while the inside of the container is sealed by the seal members.
According to the method of the prior art described above, the gap between the outer peripheral surface of the fix dummy block and the inner peripheral wall surface of the container is set so that the aluminum alloy can enter the gap between the outer peripheral surface of the fix dummy block and the inner peripheral wall surface of the container at the time of upset of the billet, but does not degrade the function of the fix dummy block, and the passage area for the exhaust can be sufficiently secured to suck air inside the container to achieve a predetermined degree of vacuum.
However, it is difficult to maintain constant the gap between the outer peripheral surface of the fix dummy block and the inner peripheral wall surface of the container because of the change with time of the gap owing to wear of the outer peripheral surface of the fix dummy block, the drop of a diameter-expanding function, adhesion of aluminum alloy dust from the container's inner peripheral surface to the outer peripheral surface of the fix dummy block, and so forth. Because the exhaust passage area changes, exhaust cannot be sufficiently conducted and variance occurs in the degree of vacuum inside the container.
It could therefore be advantageous to provide an extrusion molding method of an extrusion press that does not need to move a container and to cut and remove a discard whenever a billet is extruded, but can continuously extrude a plurality of billets by loading successively a next billet into the container and maintain stable container accuracy.
It could also be advantageous to prevent the occurrence of variance in the degree of vacuum inside a container, which variance occurs as an exhaust passage area cannot be secured and exhaust cannot be sufficiently conducted during exhaust extrusion molding by an extrusion press of aluminum alloy, or the like.
It could also be helpful to provide an extrusion molding apparatus that can conduct sufficient exhaust by securing a predetermined exhaust passage and eliminating variance in the degree of vacuum inside a container.